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Trees Cocooned in Spider Webs After Pakistan Floods

OutlineCirculating message claims that a series of attached photographs show trees cocooned in spider webs after millions of spiders climbed up into trees to take refuge from floods in Pakistan.

Brief Analysis
The photographs are genuine. A number of publications including National Geographic have reported that the widespread and prolonged flooding in Pakistan during 2010 drove millions of spiders into trees to spin their webs. While the spider theory remains the most credible, it should be noted that some commentators have suggested that the webs were made by moth larvae rather than spiders.

This is interesting – the first image doesn’t even look real! It looks like something out of an illustrated book...

An unexpected side-effect of the flooding in parts of Pakistan has been that millions of spiders climbed up into the trees to escape the rising flood waters.
Because of the scale of the flooding and the fact that the water has taken so long to recede, many trees have become cocooned in spiders’ webs.

People in this part of Sindh have never seen this phenomenon before, but they also report that there are now less mosquito’s than they would expect, given the amount of stagnant, standing water that is around. It is thought that the mosquito’s are getting caught in the spiders’ webs thus reducing the risk of malaria, which would be one blessing for the people of Sindh, facing so many other hardships after the floods.

Detailed Analysis
These eerily beautiful photographs circulate via email, blogs and social media. The description that comes with the images claims that they depict webs woven by millions of spiders that escaped to the safety of trees in response to widespread and prolonged flooding in Pakistan during 2010.

The photographs are genuine. A March 2011 report on the National Geographic website notes:

Trees shrouded in ghostly cocoons line the edges of a submerged farm field in the Pakistani village of Sindh, where 2010's massive floods drove millions of spiders into the trees to spin their webs.

Beginning last July, unprecedented monsoons dropped nearly ten years' worth of rainfall on Pakistan in one week, swelling the country's rivers. The water was slow to recede, creating vast pools of stagnant water across the countryside.

The unprecedented flooding in Pakistan in the latter half of 2010 disrupted the lives of 20 million people, but it also affected the country's arachnid population.

With more than a fifth of the country submerged, millions of spiders climbed into trees to escape the rising floodwater. As the water has taken so long to recede, the trees quickly became covered in a cocoon of spiderwebs. The result is an eerie, alien panorama, with any vegetation covered in a thick mass of webbing.

However, some commentators have suggested that the webs may have been created by moth larvae rather than spiders. Certainly, the webbing created by moth pupae such as that of the Ermine moth is reminiscent of the web covered trees shown in the above photographs. Nevertheless, it remains more likely that the Pakistan tree webs were indeed created by spiders as originally reported. Spider expert Joe Lapp reports on a similar phenomenon that occurred in Texas in 2007. In a comment on the Wired Science story about the Pakistan tree webs, Lapp suggests that the spider primarily responsible for the webs was likely to be a a Long-jawed orbweaver of the genus Tetragnatha. Lapp also suggests that the cause and effect in the reports made be wrong, noting:

We aren't seeing these webs because the spiders are escaping the flood. We are seeing these webs because the floods are producing huge numbers of flies (presumably midges and mosquitoes). The spiders that lived in these trees did tremendously well as a result.

Reports also indicate that the unprecedented spider activity may be helping to control the mosquito population in Pakistan after the flood. The Wired Science article notes:

However, the unusual phenomenon may be a blessing in disguise. Britain’s department for international development reports that areas where the spiders have scaled the trees have seen far fewer malaria-spreading mosquitos than might be expected, given the prevalence of stagnant, standing water.